httpd: if remote IP is denied, send FORBIDDEN reply earlier

httpd: if remote IP is denied, send FORBIDDEN reply earlier

While at it, fix sighup_handler to not clobber errno.

function                                             old     new   delta
send_HTTP_FORBIDDEN_and_exit_if_denied_ip              -      47     +47
sighup_handler                                        15      30     +15
handle_incoming_and_exit                            2791    2763     -28
checkPermIP                                           48       -     -48
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 1/1 up/down: 62/-76)            Total: -14 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>